The author has recruited a cohort of 15,800 women, ages 35-65, who have donated a sample of venous blood at entry in order to create a blood bank. After 64,000 person-years of followup, more than 600 cases of invasive cancers have been identified, 309 of which have been breast cancer. Of note, there has been a strong association of serum estrogens and the development of breast cancer. The investigator proposes to continue to follow the cohort prospectively in order to continue to investigate the role of reproductive hormones in cancer etiology (breast, ovarian, endometrial and large intestine) in women. The role of estrogens, androgens and gonadotropins, as well as the relationships of hormones and diet will be correlated to the development and risk of cancer. The CDMAS computer is necessary for the volume and analysis of data.